Gaseous discharge tube



A ril 1, 1958 J. w. CULP E1 AL GASEOUS DISCHARGE TUBE Filed Oct. 51, 1955 INVENTOR. JOHN w cum PAUL xosxos WILL/AM R. WHEELER ATroRNEf United States Patent GASEOUS DISCHARGE TUBE Application October 31, 1955, Serial No. 543,838

4 Claims. (Cl. 313-216) Our invention is directed toward gas filled electric discharge devices and more particularly relates to devices known as cold cathode gas diodes.

Conventional diodes of this type comprise a gas filled glass envelope in which cathode and anode electrodes are inserted. When a direct voltage is applied between these electrodes, the current flow through the tube can vary over a fairly wide range and yet the voltage drop across the tube will remain constant. This effect exists because the degree of gas ionization within the tube varies with the magnitude of current flow within the tube. As a result, these diodes find extensive use as voltage reference or voltage regulator tubes.

This conventional arrangement suffers from certain inherent disadvantages. For example, the drift voltage for a constant operating current is excessive. Further, the repeatability from repeated firings of the tube is poor. In addition, the voltage jump (any sudden change in operating voltage as the current is varied'slowly over its operating range) is also excessive. Moreover, the cathode-anode leakage resistance is too low for many applications.

We have developed a newtype of cold cathode gas diode which overcomes these difficulties.

Accordingly, it is an object of the present invention to improve the operating characteristics of cold cathode gas diodes. I

Another object is to provide a new and improved cold cathode gas diode characterized by significantly improved operating characteristics such as drift, repeatability, voltage jump,leakage resistance and the like.

Still another object is to improve the conventional type of gas filled cold cathode diode in such manner that no glass is used and the entire tube is formed from metals and ceramics.

A further object is to provide a metal-ceramic cold cathode gas diode characterized by the use of an electrically conductive tube envelope which serves as the cathode.

Still another object is to provide a new andimproved through the spacer insulator into the envelope. The anode is hermetically sealed to the insulator. The envelope is gas filled, for example, withneon or a mixture of neon and argon. When operating potentials are applied between the electrode and the envelope, the tube is rendered conductive.

In manufacturing this tube, the anode electrode is first inserted through an opening in the spacer insulator and hermetically sealed to the spacer to form an integral 1 id structure therewith. This integral structure is mounted in a jig and the metal envelope is moved into proper juxtaposition therewith. A conventional solder adapted for hermetically sealing metals to ceramics is then placed in position in contact with both the envelope and the spacer. This entire arrangement is placed in a vacuum chamber and the chamber is then evacuated. At this point, the envelope is not hermetically sealed to the insulator; as a result, when the chamber is evacuated, the tube envelope is alsoevacuated.

An inert gas or mixture of inert gases is then introduced into the chamber and infiltrates into the tube envelope. The entire structure is then heated, for example, through the use of induction welding techniques, to melt the solder and to produce the desired hermetic seal between the tube envelope and the insulator.

The tube thus formed requires no exhaust tubulation; it can be produced easily and inexpensively and its operating characteristics, particularly drift, repeatability, voltage jump and leakage resistance are superior by factors ranging from three to five as compared to conventional tubes.

Further details in our invention will 'now be explained with reference to the accompanying figure which is a cross sectional view of our tube.

A molybdenum cup-shaped envelope 10 is hermetically sealed at 11 to analuminum oxide spacer insulator disc 12. A molybdenum rod 13 is inserted through an orifice 14 in the insulator and projects inwardly into the envelope. The anode rod is hermetically sealed to the insulator. The envelope itself is filled with an atmosphere composed of 99% neon and 1% argon. The opening 14 in the disc through which the anode rod extends into the tube envelope opens or flares to an enlarged cylin drical or funnel shaped well or section 15. The rod is separated from the walls of this cylindrical section. The envelope is connected as the cathode and the rod is connected as the anode and operating voltages are applied in conventional manner. M

This tube must be aged in accordancewith techniques Well known to the art. During aging and also during normal tube operation molybdenum will sputter onto the surface of the insulator. If at the inner surface of the disc 12, the anode is in contact with the disc (the cathode envelope of course is also in contact with the inner surface), the anode-cathode separation, taken along a path on the inner surface of the disc is small. The sputtering action can then establish an electrical connection between the electrodes and cause malfunctioning of the tube. The presence of the enlarged cylindrical section effectively lengthens this path to an extent at which such an electrical connection cannot be established. Moreover, when the length of the enlarged section is sufiiciently high, no sputtered metal can penetrate to the bottom of this section. Other means can be used to lengthen this path. For example, the inner surface of the disc, instead of being smooth can have recessed grooves of channels.

Informing this tube, the rod is first inserted into the disc orifice and hermetically sealed thereto through the use of conventional ceramic metal sealing techniques. This assembly is then mounted in a jig, the tube envelope is moved into position, and a ring of titanium-silver-copper solder is slid over the envelope down to the surface of the disc. This entire structure is then placed into a bell jar, and the jar is then evacuated to a pressure of approximately .03 micron of mercury. As indicated previously, the tube envelope is also evacuated at the same time. A gas mixture composed of 99% neon and 1% argon is then introduced into the bell jar in suificient amount to produce a gas pressure of millimeters of mercury within the tube envelope. The structure is then Patented Apr. 1, 1958.

a1. mm

induction heated (by means of a work coil positioned about the outside of the bell jar) to a temperature on the order of 1950 C. to melt the solder and form the desired ceramic-metal seal. After the tube has been hermetrically sealed and cooled, the gas pressure within the tube was reduced to about 25 millimeters of mercury.

A tube of this kind provided with a molybdenum envelope .260 inch in diameter and .437 inch long sealed to an insulated spacer having a .295 diameterand containing a centrally positioned anode rod electrode .040" in diameter was produced in the manner indicated.

When a plurality of these tubes were rendered operative, it was found that (a) the maximum ionization voltage required was 127 volts, the average ionization voltage being about 125 volts; (b) the average operating voltage for a current of 2.5 ma. was found to be 84.5 volts (the maximum-minimum range of the operating voltagefell within the limits of 83 to 87 volts); (0) the regulation has a maximum value of 1.8 volts and an average value of 1.2 volts; (d) the maximum drift was found to be 35 millivolts, the average value of drift being 10 millivolts, (u) the repeatability has a maximum range of 5 millivolts and an average value of 2 millivolts, (f) the maximum voltage jump was found to be less than 1 millivolt and (g) the leakage resistance has a magnitude in excessof 10 ohms.

While we have shown and pointed out our invention as applied above, it will be apparent to those skilled in the art that many modifications can be made within the scope and sphere of our invention as defined in the claims which follow.

What is claimed is:

1. In combination, an electrically conductive cylindrical hollow tube envelope open at one end; a ceramic base hermetically sealed to said envelope .to close said open end, said base being provided with a conically shaped channel extending therethrough, said channel being aligned with the axis of the cylindrical envelope, the larger end of said channel communicating with said envelope; and an electrically conductive electrode projecting through said channel into said envelope and hermetically sealed to said base, said envelope being filled with a mixture of argon and neon gases.

2. The combination as set forth in claim 1 wherein said electrode is sealed to said base at a position adjacent the smaller end of said channel.

3. A cold cathode gas filled diode comprising a cylindrically shaped hollow molybdenum cathode envelope; a rod shaped molybdenum anode electrode; a ceramic base hermetically sealed to said envelope and provided with a conically shaped channel extending thcrethrough, the larger opening of said channel communicating with said envelope, said anode electrode projecting through said channel into said envelope and being hermetically sealed to said base, said envelope being filled with an inert gas mixture containing 99% neon and 1% argon.

4. In combination, an electrically conductive cylindrical hollow tube envelope open at one end; a ceramic base hermetically sealed to said envelope to close said open end, said base being provided with a centrally positioned channel which extends through said base to communicate with said envelope, said channel being flared in such manner that the channel opening communicating with the envelope is large compared with the channel opening remote from the envelope interior; an electrically conductive electrode extending through said channel into said envelope and being hermetically sealed to said base in a region adjacent said remote channel opening, said envelope being filled with a mixture of argon and neon gases, said large channel opening lengthening the electrical path taken along the base surface adjacent said envelope between the envelope and said electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,324,557 Claesson July 20, 1943 2,417,361 Herzog Mar. 11, 1947 2,428,610 Beggs Oct. 7, 1947 2,523,287 Friedman Sept. 26, 1950 2,735,954 Rawls Feb. 21, 1956 FOREIGN PATENTS 533,107 Great Britain Feb. 6, 1941 

